A molding member of the type defined in the opening sentence is known from U.S. Pat. No. 4,185,955. Said document describes a mold having two mold sections which, if the mold sections are in contact with one another, bound a disc-shaped cavity for molding an optical disc. Each mold section has a molding member comprising two plates, grooves being provided in the contact surface of one of the plates to form cooling ducts for rapidly cooling the injection-molded product and the molding members after the injection-molding process. The plates of a molding member are secured to one another by means of bolts. To seal the cooling ducts O-rings are provided in grooves formed especially for this purpose in one of the plates. This method of joining the plates requires much space. The plates should have an adequate thickness to allow them to be provided with the required screwthread. The bolted joints are situated near the edges of the plates at some distance from the cooling ducts because the space available between the cooling ducts is not adequate and because seals in the form of O-rings have to be inserted between the cooling ducts and the bolted joints. In order to prevent the plates from being warped because of the liquid pressure in the cooling ducts, as a result of which the wall of the cavity in which the product is molded would no longer have the required flatness, the plates should have a specific thickness (rigidity). Because of these requirements the molding member is large, which also results in large dimensions of a mold, cooling ducts, liquid pumps, hydraulic cylinders for moving the molding member, and other parts of an injection-molding apparatus in which the mold with the molding members is used.